William Crabtree, Venus genius

Until 1609, the way in which the planets moved was not clearly understood. Did they orbit the Earth, as thought from time immemorial, or did they orbit the Sun, as suggested by Copernicus in 1543?

On the Continent, Johannes Kepler favoured the Copernican system. In 1609 he showed mathematically, based on the accumulated observations of the Danish nobleman-astronomer, Tycho Brahe, that the planets indeed orbited the Sun, as did Earth. For the last year of Tycho's life, 1600-1601, Kepler had been his assistant at Prague. In 1619 Kepler published his Rudolphine Tables of planetary motion and predicted a very rare transit of Venus, a line of sight effect as seen from Earth, across the face of the sun for 1631. Although watched for by Gassendi, in France and from central Europe it occurred at dawn and was not seen. A rare chance was apparently lost for generations to come.

But about seven years later it was suggested by William Crabtree (1610-1644) of Broughton Spout, Salford, in correspondence with his friend Jeremiah Horrocks (1619-1641) then living at Toxteth near Liverpool, that careful telescopic observation of the planets, especially Venus, Jupiter and Saturn might refine Kepler's predictions (Laws) of planetary motion. In 1639, based on their new positional observations, Horrocks predicted another, hitherto unexpected transit of Venus for Sunday 24 November 1639 (O.S. Julian calendar, now 4 December in the modern, post 1752, Gregorian calendar.) Horrocks's new calculations had shown that transits of Venus occur in pairs separated by 8 years, and then a longer gap of 122 years. Here was the opportunity of a second bite at the cherry, now thanks to two Lancashire astronomers.

Horrocks, now living with the Stones family (like Crabtree they were haberdashers) at Carr House at Bretherton, not far from Preston, began his observations on the Saturday but saw nothing. The following day he had to attend to his church duties at St. Michael and All Angels half a mile away in Much Hoole but returned home in the afternoon to witness Venus already encroaching onto the solar disc. The time was 3.15pm and the sun was setting in a partially cloudy sky. He recorded another observation at 3.35pm and the last at 3.45pm before the sun set. At Salford, William Crabtree made a single observation at about the same time. They were both surprised at the smallness of the planet silhouetted against the face of the sun. The usually brilliant planet seen in the evening or morning twilight suggests a much bigger physical size but here, for the first time, it fell to Horrocks and Crabtree to put it into a truer scale. Crabtree's observation actually gave a more accurate size determination for Venus than did Horrocks's. It should be noted however that their observations were not sufficient to put an absolute scale to the size of the solar system. That was to come much later, based on measurements made during subsequent transits of Venus in the 19th Century.

Jeremiah Horrocks is seen as the grandfather of British astronomy, but Crabtree's contribution was crucial. Born in Broughton, now part of Salford, in 1610 and educated at Manchester's Grammar School (now Chetham's School of Music), Crabtree was a cloth merchant and had money and spare time to practice his favourite hobby - astronomy. William Crabtree was therefore one of only two people to spot the first recorded transit of Venus in 1639, but he remains the unsung hero of the event; an event which gave birth to UK astronomy. Transits of Venus happen only rarely and the last occurred 8 June 2004. The most recent transit prior to 2004 was in 1882. The next transit happens in 2012 after which we will not see another for more than a century.

Crabtree and Horrocks corresponded extensively by letter from about 1636 until 1641. Although there is some uncertainty if they ever met, considering the likelihood that they were introduced by John Worthington, also studying with Jeremiah Horrocks at Emmanuel College, Cambridge (ca1634-1636), and the son of another Manchester cloth merchant, it would be surprising if Horrocks didn't occasionally call in at Salford to see his friend Crabtree enroute between Cambridge and Toxteth. Horrocks certainly planned to visit Crabtree on 4 January 1641 but didn't show up; he had died suddenly the previous day, 3 January 1641 (O.S.). Crabtree died three years later, in 1644, during the Civil War and is buried somewhere within the precincts of Manchester's Collegiate Church, now Manchester Cathedral.

The next Venus transit will take place on 6 June 2012, after which there will not be another until 2117.

Astronomer William Crabtree of Broughton recognised

The 19th century painting by Ford Maddox-Brown, showing Crabtree's observation of the transit of Venus in 1639, hanging in the great hall of Manchester Town Hall does not accurately depict a twenty-nine year old astronomer with his family and has to be considered in context as a stylised Victorian perception of Manchester's history. By comparison, Jeremiah Horrocks was given a memorial in Westminster Abbey. To date, December 2009, neither scientist is acknowledged in Manchester's Museum of Science & Industry (MOSI) although in June 2004 public lectures about the transit of Venus were given at MOSI by Kevin J Kilburn FRAS of Manchester Astronomical Society whose members also observed the transit of 8 June from the Godlee Observatory.

In June 2004 a commemorative street nameplate (see picture below) in memory of William Crabtree was unveiled at the junction of Lower Broughton Road and Priory Grove. This site marks the location that is thought most likely to have been the home of Crabtree and his family at the time when he was working with Horrocks. The Mayor of Salford, Councillor James Hulmes, and members of the Salford Astronomical Society were in attendance.

Local residents Carl Barry and Lilian Fletcher have compiled a detailed account, available below, of the events leading up to the unveiling of the new street nameplate.

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